The present invention relates to the preparation of dye-containing compositions. More particularly, the present invention relates to dye-containing compositions and methods for the preparation thereof, in which the dye is copolymerized with an acrylic based monomer to form a hydrophilic polymer in which the dye is present in a non-diffusible form. The dye - acrylic polymer composition can be produced in the form of microbeads by emulsion (water-in-oil) polymerization.
Previous methods for the bonding of dyes with other molecules include such known procedures as the use of a Mannich - type reaction, i.e., formaldehyde condensation of the dye with an amine group, as in preparation of the complexones. Such reactions are described, for example, in the following publications: R. O. Cinneide, Nature, 175, 47 (Jan. 1, 1955); R. Prible, Analyst, 83, 188-95 (1958); Swiss Patent No. 298,194 (July 1, 1954); U.S. Patent No. 2,745,720; and G. Schwartzenbach et al., Complexometric Titrations, Methuen Press (Barnes and Noble), 1969. Such publications do not refer to attaching dyes to polymers. A widely used method, with several commercial sources, for attaching phthalein type dyes to other moieties, is that in which an isocyanate group on a dye reacts with an active hydrogen on another moiety in non-aqueous media. Such a method necessitates a special synthesis of each dye, with formation of the attached isocyanate group during synthesis. Another approach which attaches the dye to a polymer is to derivatize the polymer, i.e., attach groups such as an amino group to the polymer so that the dye can be subsequently reacted, such methods being described for example, by J. K. Inman et al., Biochemistry, 8, 4074-82 (1969). These techniques require prior formation of a polymer, with subsequent dye attachment.
Various dye compositions are also described in U.S. Pat. Nos. 4,016,133 and 4,017,476. In U.S. Pat. No. 4,016,133, there is described a process in which a dye molecule is combined with monomers to result in a chemical combination of the dye with the resulting polymer. The method of this prior art patent emphasizes the requirement of including a particular type of monomer, monomer C, which has an affinity for the dye, in the mixture of monomers, A, B and C. A large number of different dye chemical types are mentioned, essentially any water soluble fluorescent dyes. Thus, a specific type of attachment of the dye to monomer C is not required. Also, this prior art patent does not state that the dye is of a type which copolymerizes, as a monomer itself, but only that the dye combines, during polymerization, with a monomer for which there is an affinity. This prior art method is thus distinguished from the present invention which is directed to the use of specific dyes which copolymerize with a single other monomer, which by itself has no dye affinity. Also, in the present invention, the dye becomes part of the polymer chain by reason of its ability to act as a component of the polymerization process.
In U.S. Pat. No. 4,017,476, a polymer of a very specific type is formed in the usual way from a monomer, but the polymer forming reaction, i.e., formation of molecular chains, is not ended in the usual way, but rather the polymer is left with reactive sites, i.e., reactive ends of the chains, which will react with a subsequently added dye molecule to combine the dye chemically with the polymer. This prior art method is distinguished from the present invention in which the dye is included in the monomer solution so that the dye molecule is essentially another monomer which becomes a part of the chain during polymerization. Thus in effect, this prior art patent covers methods of treating a preformed polymer in such a manner that dyes combine with it. Such a prior art method is not a copolymerization with the dye as is the method of the present invention.
By the present invention, there is provided a method for the preparation of a dye - containing composition, in which the dye is copolymerized with an acrylic based monomer to form a hydrophilic polymer in which the dye is present in a non-diffusible form. The present invention includes the dye during polymerization, and is thus simpler than prior art procedures. Also, the present invention is applicable to aqueous polymerization of hydrophilic polymers. The dye - acrylic polymer composition can be produced in the form of microbeads by emulsion (water-in-oil) polymerization. An additional feature includes the incorporation of light scattering particles in the form of a material such as polystyrene microspheres with the dyed polymer microspheres.